1. Field of the Invention
The present invention relates to a gripper used in an automatic bag filling apparatus for griping side edges of a bag.
2. Related Art
An intermittently rotating table type bag filling apparatus, for instance, is equipped with a table that rotates intermittently and a plurality of pairs of grippers that are installed around the periphery of the table at equal intervals and rotated intermittently together with the table. In this bag filling apparatus, while the table is making one rotation, one bag is supplied to the grippers, and the filling process that includes opening of the bag mouth, filling of the bag with contents, and, if necessary, sealing of the bag mouth, is performed with the bag being gripped at its both side edges by the grippers and hanged from the grippers.
Japanese Patent Application Laid-Open (Kokai) No. 1994-156440 discloses one example of grippers for an intermittently rotating table type bag filling apparatus, in which the grippers are comprised of: a pair of left and right swing levers mounted on an intermittently rotating table, gripper arms whose base end portions are respectively affixed to the swing levers, chuck sections provided in the tip end portions of the gripper arms to face inwardly and face each other, and a chuck open/close mechanisms that open and close the chuck sections. In this gripper, the chuck section is comprised of a fixed chuck element having a gripping part affixed to the gripper arm tip end so as to face in the direction opposite from the gripper arm base, and a movable chuck element installed at the tip end of the gripper arm so as to be rotated; and the chuck open/close mechanism is comprised of (a) a drive mechanism installed at an appropriate location on a base frame of the bag filling apparatus (for example, at the location where empty bags are supplied, or at the location where filled bags are discharged), (b) a link mechanism that includes, among others, rods, links and a passive member installed on the gripper arms and transmits the force of the drive mechanism to the movable chuck element, and (c) a spring installed on the gripper arms and constantly pushes the movable chuck element in the direction of closing.
However, this chuck open/close mechanism has several problems.
(1) A plurality of drive mechanisms must be installed on the periphery of the underside of the table, and thus the mechanism takes up spaces, makes the structure more complex, increases the costs, and makes cleaning and maintenance more difficult.
(2) When a process to remove defective bags, a process to re-hold and weigh the bags, or the like, is added, and the chuck sections must be opened and closed once at a location where the process is executed, and this requires the drive mechanism for the chuck open/close mechanism to be linked (via a cam or the like) mechanically to the main (i.e., rotating table) drive mechanism, resulting in that it becomes difficult to change the design or to make modifications in order to newly install a drive mechanism, and adding the above-described processes is in itself difficult when there is not enough space on the frame of the bag filling apparatus.
(3) Though it is desirable to vary the gripping force of the chuck section depending on the material and thickness of the bag and depending on the amount of material to be filled in the bag, it is extremely difficult to replace the springs used in the chuck sections, and even skilled technicians require some time to do this.
Japanese Patent Application Publication (Kokoku) No. 1995-37251 discloses a chuck open/close mechanism that includes a linking mechanism of a toggle system instead of springs; and this mechanism has the same sorts of problems as that of the system disclosed in Japanese Patent Application Laid-Open (Kokai) No. 1994-156440.
Japanese Utility Model Application Laid-Open (Kokai) No. 1983-49706 and Japanese Patent Application Laid-Open (Kokai) No. 1980-20178 disclose bag filling apparatuses in which the movable chuck element is driven by a single-acting air cylinder.
The bag filling apparatus disclosed in Japanese Utility Model Application Laid-Open (Kokai) No. 1983-49706 is an intermittently rotating table type bag filling apparatus; and in this apparatus, air cylinders are installed in the space which is next to each gripper arm on the intermittently rotating table; accordingly, the space occupied by each gripper pair is much greater, and the number of gripper pairs that are installed on the table is limited; and if the number of gripper pairs is to be increased, then the table (and as a result the entire bag filling apparatus) needs to made larger. There is no description in Japanese Utility Model Application Laid-Open (Kokai) No. 1983-49706 about the supply of bags; however, in the apparatus of this relevant art, the fixed chuck elements are installed on the outside of the movable chuck element (when viewed from the center of the table); accordingly, the gripper arms must be opened and closed in order to prevent interference between the fixed chuck elements and the bag when bags are supplied from the outer circumference of the table. This decreases the productivity due to the time required to do so. Furthermore, in the bag filling apparatus of this relevant art, the linking mechanism that links the air cylinder and the chuck section is exposed; accordingly, it is susceptible to becoming dirty, and the apparatus is low in cleaning and maintenance characteristics.
Japanese Patent Application Laid-Open (Kokai) No. 1980-20178 relates to a fixed bag filling apparatus and describes driving the movable chuck element with a single-acting air cylinder. In this bag filling apparatus, since the fixed chuck element is provided on the empty bag supply apparatus side, practically there is a high risk of the fixed chuck element interfering with the bags that are being supplied, and it may be necessary to have a sliding body (17) (an element that corresponds to the gripper arm) to avoid this. Thus, when the technology of Japanese Patent Application Laid-Open (Kokai) No. 1980-20178 is applied to, for example, an intermittently rotating table type bag filling apparatus, problems similar to those seen in Japanese Utility Model Application Laid-Open (Kokai) No. 1983-49706 would occur. Furthermore, in the apparatus of Japanese Patent Application Laid-Open (Kokai) No. 1980-20178, a rack and pinion mechanism is provided between the air cylinder and the chuck section (an element that corresponds to the mechanism linking to the chuck section), and this rack and pinion mechanism is exposed; accordingly, dirt tends to collect there, lowering the cleaning and maintenance characteristics.